Fluid hydroforming



p 1956 J. F. SNUGGS ETAL FLUID HYDROFORMING Filed Oct. 27. 1951 Charge Fig. 2

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United States Patent FLUID HYDRQFORIVHNG John F. Snuggs and Charles M. Walker, Chicago, IlL, assignors to Standard Gil Company, Chicago, EL, a corporation of Indiana Application October 27, 1951, Serial No. 253,498

7 Claims. (Cl. 196-50) This invention relates to fluid hydroforming and it pertains more particularly to an improved method and means for treating hydrocarbons of the naphtha boiling range with solid catalyst of small particle size in the presence of hydrogen, by a fluidized solids technique for efiecting hydroforming, i. e. octane number improvement, dehydrogenation, aromatization, isomen'zation, desulfurization, etc.

Heretofore, fluidized solids technique has been extensively employed for effecting catalytic cracking of gas oils and to some extent for effecting reforming of lower boiling hydrocarbons. Hydroiorming has been commercially employed in fixed bed units and although it has often been proposed that fluidized solids technique be employed for effecting hydroforming it has been recognized that hydroforming presents certain problems that are not encountered in catalytic cracking. High catalyst to oil ratios are desirable in catalytic cracking but when employed for fluid hydroforming they result in a degradation of product quality and/or yields. Much longer contact times are required for hydroforming than are desirable for catalytic cracking and since the former process is likewise endothermic, a problem arises as to the provision of the required amount of heat in a fluid hydroforming reactor. While cracking catalyst is effective in its fully oxidized state as it leaves the regenerator, hydroforming catalyst requires some degree of reduction or conditioning. Hydroforming requires high pressures usually of the order of 100 to 500 p. s. i. which in turn creates problems of overcoming erosion and catalyst losses when catalyst-containing fluids are depressured. In catalytic cracking, if some hydrocarbon material from the reaction side gets into the regenerator, it merely burns therein, but if appreciable amounts of hydrogen should find their way into the regenerator, the operation would be more hazardous. An object of our invent-ion is to provide a method and means for solving these and other problems presented by the application of fluidized solids technique to hydroforming.

When charging high sulfur naphtha, it has been found that when regenerated hydroforming catalyst is contacted with hydrogen, there is not only a formation of water vapor, but there is a liberation of sulfur dioxide apparently by replacement of adsorbed sulfur dioxide with hydrogen. A more specific object is to avoid the presence of water and sulfur dioxide in the dense catalyst phase in the reaction zone as well as to avoid-introduction of hydrogen streams into the regeneration zone while minimizing the overall depressuring requirements.

Another object is to avoid cracking in the upper dilute phase portion of the reactor. A further object is to avoid short circuiting of regenerated catalyst back to the regeneration zone while obtaining benefit of high temperature hydrogen stripping of withdrawn catalyst. Other objects will become apparent as the detailed description of the invention proceeds. i

In practicing our invention, we employ a tall vertical reactor whose height is preferably about to 15 times 2 its diameter. superheated hydrogen, preferably a-'recycle gas stream, at a temperature of about-D to 1300 F., is introduced at the base of the reactor and distributed across the cross-sectional area thereof. Catalyst is introduced at a higher level after it has been contacted with hydrogen for the time required to reduce it to the desired lower state of oxidation. Charging stock vapors are introduced into the reactor ata level spaced from the hydrogen inlet by about .5 to 2 reactor diameters so that below the charging stock inlet the catalyst will contact only the superheated hydrogen. A deep dense phase turbulent catalyst bed is maintainedin the reactor at a depth sufiicient to give the required contact time which in the case of molybdcna-on alumina catalysts is approximately one minute, the ratio of charging stock to hydrogen being at least as great as heretofore employed in fixed Ibed operations, e. g. about 1 to 10 or about 5 mols of hydrogen per mol of charging stock introduced.

The regenerated and reconditioned catalyst is introduced at a low rate so that of materials charged to the reactor the catalyst to oil weight ratio is in the range of .1 to l, e. g. about .35. Catalyst is withdrawn ata corresponding rate directly from the dense phase at a point below the charging stock inlet and spaced from the point of catalyst inlet so that short circuiting of regenerated catalyst may be avoided while at the same time the withdrawn catalyst will be partially stripped by superheated hydrogen immediately prior to its withdrawal. The withdrawn catalyst is preferably conveyed by steam or hot hydrogen through an internal or external riser to an elevated stripper so that the necessary catalyst head is obtained for introducing catalyst from the stripper to the reg'enerator. Stripping gas from the top of the stripper is returned to the dilute phase in the reactor above the dense turbulent phase and it helps to sweep out reaction products, thus minimizing product holding time in the upper part of the reactor. Cracking in the upper part of the reactor may be further minimized by cooling the stripping gas before its introduction in the upper part of the reactor and/ or by introducing a portion of the liquid product or cooling water which can be vaporized in the dilute phase and thus provide some cooling in addition to providing a sweeping action for product removal.

Stripped catalyst is regenerated with an oxygen-containing gas such as air in a relatively small re'generator be introduced into the dilute phase portion of the reactor so that it does not pass through the dense catalyst phase therein. By this method of operation, no hydrogen stream is introduced into the regenerator and any cata lyst particles entrained in the stripping gases are recovered without the necessity of employing additional catalyst recovery and depressuring equipment. Apre ferred method of operation is to introduce the-partially reduced catalyst above but'near the oharging'stock-inlet and to withdraw spent catalystat a spaced pointin the reactor from a level below the charging'stock-inle'L- The invention willbe more clearly understood from the followingdescription of a specific example thereof read in conjunction withthe accompanying drawings in which:

- catalyst lift structure.

l is arschematic "flow-diagram of a 2,000 barrel per day fluid hydroforming unit embodying our invention;

Fig. 2 is a schematic flow diagram of an al ernative system;:and' r 'Fig. 3 --is -a detailed section illustrating a particular The invention will-be described as applied to "the hydroforming ofr53 A5121. naphthaof low sulfurcontent boilin g -in the range of about 200 to 330 F ha'ving j a C; FQR. R octane numbenof about 60 with a molybdena-on alumina catalyst h-avinga -particle size ranging be. understood "that" any known hydroforming or hydro fining catalyst-may be employed. The contact time and operating conditions willbe dependent, of c0urse,on the particular catalyst and its activity (as wellason the charging stock and nature of results desired); platinumcontaining catalyst (U. S. 2,'479,109-l0)' may-require somewhat lower temperatures and lower contact time than'a-molyhdena-alumina catalysts. Other group VI metal. oxides or sulfides on gamma-alumina supports may: be employed either with. or without added group VIII metal oxides or sulfides such as: nickel or. cobalt oxides 10f? sulfides, examples of mixed catalysts being1the so-:cal led.cobalt molybdate;catalysts, nickel-tungstate, etc., with-more or lessof the oxygen replaced by sulfur.

. :1 Fresh .or make-up catalyst-is preferably-introduced a temperature not substantially higher than about 11507 F. The preconditioning vessel 27 in this embodiment-is an upwardly extending pipe about 2 feet in diameter which is Within the reactor vessel 31 and which has a catalyst discharge opening 32 about 5 feet from distributor grid 33 in the lower part of the vessel. Preconditioning vessel 27 is thus of such size -.as to provide for partial reduction of the catalyst before the regenerated catalyst is admixed with the dense catalyst phase in reactor 31,

said conditioning usually requiring at leastabout-Seec; onds and a period of about secondsbeing generally sufficient. During the partial reduction of ,theicatalyst,

water vapor is liberated and when the charging stock Reactor 31in this case is a lined vessel with aS 'foot 3 inch I. D. lining in about a 7 foot I. D..shell about-60' Charging stock vapors are --intr oduce'd''byfeet tall. line by any'lrnown distributingmeans-SG or'siuiply at Sor 4 spaced points at a level at least aboutone half reactor diameter butwithin two diameters from the botintolthe system by line 10 into regenerator 11,: which in this case maybe a thermally lined vesseluwithabout a 3 foot .L 'DVshell; 2toot, 3 inch '1. D. lining, Zlfeethigh, superimposed by a separation zone about 3 .feet larger in diameter by about 5301' dfeet-in height. :A number of {filters 32 are provided :in the upper enlarged :section with provision for periodic-blow back of a portion thereof swim-preheated air introduced throughline 13, the

vented catalyst-free gas being passedsthrough' reducing valvenl4 and thenrlvented by linelSto. an appropriate flue. The lower part of the regenerator 11 is provided withecooling :tubes: :16 .so' that cooling water introduced through line 17 to separator :18. flows through line 19 :to adowertube header,xtheuce through tubes :16 and :line -20; back to=separator 18, 'the'generated'stearn heingiwithdrawn through .line'. 21. Air for efiecting regeneration isein'troducedthrough line,22 and. is distributed across thefregeuerator by grid 23.' .-Inthis example during noroperation-about .114 mols.;per. hour .(about 3270 pounds ';per' hour) of air is thus introduced through -:line

22-under. a pressure'ofabout270 p;s..i.g.:soi thatsardense turbulentcatalystphasei is maintained with/its upper level preferably .below the top of tube -1 6at .a' temperature of 'approximately 1.10091? 1 flatalystis withdrawn fromzthe lower pastof the dense iphasedn the regenerator 11 above .igrid .23 by linear standpipe 24 :in :amounts regulated by waive :25,'.1an.;inert aeration .gas beingintroduced thr0ugh.;line .126i-as 1 TO: quired. nDuring continuous operation, the::amount of catalyst thusswithdrawn :may be approximately '8000 poundstper houn- Q This catalyst iszcarried aupwardly; into preconditioning .vessel; 27-by1neansof hotshydrogen from line .28. Thisihot hydrogencmay 'consistrs'olely of .preheated 'hydrogemrecyele gas fromiline;29. orzit: mayrbe superheated :hydrogenaat about 1200.:to. 13.00 from 30 and-.Sflficritumay bea mixture :thereofiiitusually being desirable to vefiectzconditioning ;the;;oata1yst-;at

reactor.

tom of the reactor vessel. Thus thatportion-of the' dense catalyst phase in the reactor'which is belowthe chargingstock inletlevellafijis contacted only withjthe supere heated hydrogen Which-is introduced at the basei of the vessel through line 39. Catalyst beneath thechar'ging' stock inlet is subjected to the stripping action of superheatedhydrogen and at the same time the turbulence j 33 below .chargingstock inlet-36 andspaceddrormcata .lyst inlet 32, provides-for withdrawal of catalyst for trans fer withihot hydrogen from line 38 through. riser 39 to stripping chamber 46, which is preferably superimposed i above the reactor. vThe lift gas-for transferringcatalyst may be steam instead of'hot hydrogen. Riser E39may beza 2inch pipe flaredand reinforced at:its bottom-Etc cooperate with tapered plug'41.which*may:be moved Ytoward or 1 away from the bottom of pipe 39 and through which thetcarrier .gasisv introduced,.as shown in greater detaillin Fig. 3. :Itfshould .be understood, of 'cou'rs'epthat an external riser line may be employed insteadofzanrin ternal .line for;conveyi ngcatalyst from :the loweriapart of the reactor tothe stripper preferably. t an intermedi,

ateleve zl'therein. v r

The. stripper or '.spent:catalyst 'hopper illz may 'sgbea ap-v proximatelylfeet in diameter by. about .26ifeet fin height,

and may be provided with adishibutor grid .42 atiits base and an .inlet .43 :for introducing steam, :hot hydrogen or inert" gas to .Eserveras:v an :aeration oradditional stripping I medium. "Strippedrcatalyst flows from the lower-rpart of. the :stripper. through 1 standpipe line :.44 ;.and--r,control valve 44a preferably to intermediate level inIegcneraF tor .11. Overhead gas from the}: stripper passes rbyzaline 45 T10; the :;upper :part of the: reactor 31;, above the dense phase level-therein and ifdesired itmay be passed through cooler "46 for, loweringzthe temperaturesof f the dilute phase :the "reactor. :so'rthat .thermal cracking-will .be minimized. A quenchtliquid such for example .as apolition of .the liquidxproducruneven-water -:may-:be intro ducedlabove the: dense phase through line .147 :.for vaporization :and removal with'the product :stream to 'senyexthe double] purpose of icooling: thezrreaction products minimizing their residence; time; in; the.:11ppe.r partuofithe per cubic foot.

Reaction products are withdrawn from the upper part of the dilute phase in reactor 31 through cyclone separator 48, dipleg 49 of which extends into the dense phase for returning separated catalyst particles thereto. The product stream then passes through line 50 andheat exchanger 51 to product recovery system 52 in which recycle hydrogen containing at least about 60% hydrogen is separated at substantially reaction pressure and recycled by line 53 through heat exchanger 51 for heating it to a temperature which in this case is approximately 700 F. This recycled hydrogen stream provides the hot hydrogen for introduction through line 29, and optionally through lines 38 and 43, and line 29 may communicate with line 53 by line 54. Most of the hot recycled hydrogen passes through line 56 to hydrogen superheater 57 wherein the hydrogen is superheated to a temperature of about 1200 to 1300" F. for return by line 30 to the base of the reactor.

In this example, the naphtha charge is introduced at a temperature of about 850 to 1050 F., e. g. about 950 F., at the rate of approximately 2000 barrels per day or approximately 22,350" pounds per hour. Superheated hydrogen is introduced at the base of the reactor at about 1200 to 1300 F. at the rate of about 1300 mols per hour or approximately 18,000 pounds per hour. The reactor bed depth in this case is about 54 feet and its average temperature about'930 F., the upward gas velocity being in the range of .5 to 1.5 or in this case .84 feet per second to give a catalyst bulk density of about 30 pounds Thus the charging stock contact time is approximately one minute, the weight space velocity being about .45. From the pressure balance standpoint, the pressure immediately above grid 23 and regenerator 11 may be about 265 p. s. i. g., immediately above the grid in the reactor about 261' p. s. i. g., at the top of the reactor (and top of the stripper) about 250 p. s. i. g., at the bottom of the stripper about 254 p. s. i. g., at the bottom of transfer line or standpipe 44 about 268 p. s. i. g. (immediately above control valve 44a at point of aeration), and at the top of the regenerator about 261 p. s. g. It will be understood, of course, that'control valves and aeration line will be employed in accordance with usual fluidized solids practice throughout thesystem.

,fSinceno invention is claimed in the product recovery system per se, it requires no detailed description;- Generally speaking, however, the product stream after passage through heat exchanger 51 may be further cooled by heat exchange with incoming charge and introduced into a baffled scrubbing section in a fractionating tower operating at substantially reaction pressure (about 240 p. s. i. g.) and with a top temperature of 270 F. and a bottom temperature of 420 F. Catalyst particles are removed in heavy condensate and may be recycled to the reactor. The overhead from this fractionator may then be condensed and the recycle hydrogen separated therefrom for compression and recycling through heat exchanger 51. So-called polymer may be recovered from high boiling material leaving the first fractionator and the unrecycled portion of the separated hydrogen may be scrubbed with incoming charging stock for recovery of gasoline boiling range components therein. The charging stock is then vaporized and heated to a temperature of about 900 to 1050" F. for introduction into the reactor as hereinabove described.

In the system herein described, the dry gas production may be about 12 weight per cent, polymer about 3.5 weight per cent, and butane-containing gasoline about 84 weight per cent, the coke formation being only about .5 weight per cent, about of the total gasoline fraction being butanes. The product gasoline is substantially free from sulfur and has a C. F. R. R. octane number of about 95 to 100 (based on product gasoline containing only a small part or" the butanes with a maximum boiling point of 400 F. and a 90% point of about 300 F.).

In Fig. 2, the system is essentially as described in connection with Fig. 1 except that the catalyst conditioning vessel 27 is outside of the reactor, catalyst being introduced from the conditioning vessel 27' to the reactor by conduit 32 and conditioning gases containing water and S02 being introduced to the upper part of the reactor by line 34. Also in this example, the stripping gas from the upper part of the stripper 40 is returned to the space above the dense phase in the reactor by internal line 45. Other modifications and alternative arrangements of apparatus will be apparent from the above description to those skilled in the art.

While in the above examples a light naphtha is contacted with a molybdena-alumina catalyst at a temperature of approximately 930 F. in the reactor, itwill be understood that the temperature, pressure, catalyst to oil ratios and space velocities will be dependent on the particular charging stocks and catalysts employed and upon the nature and degree of hydroforming which is to be attained. 7

We claim:

1. The method of efiecting fluid hydroforming which comprises superheating a hydrogen gas stream to a temperature of about 1200 to 1300 F. and introducing the superheated stream at the base of a reaction zone having a height about 5 to 15 times its diameter, distributing the superheated hydrogen across the base of said zone'into a unitary fluidized catalyst bed which extends to the upper part of the reaction zone, introducing superheated charging stock vapors containing a small amount of sulfur directly into said bed at a level spaced from the hydrogen inlet by about one-half to two reactor diameters, introducing conditioned catalyst at the lower part of the catalyst bed, employing an upward gas velocity in the reaction zone to maintain the catalyst in dense phase fluidized condition and to give abed depth for obtaining effective hydrotorming of the charging stock at a temperature in the range of aboutSSO to 1000 F. under a pressure of about to 500 p. s. i. g., withdrawing catalyst from the dense phase at a level below the charge inlet and from a point spaced from the catalyst inlet, conveying the withdrawn catalyst to a stripping zone and contacting it therein with a stripping gas, introducing gas from the upper part of the stripping zone to the upper part of the reaction zone above the dense phase level therein, withdrawing catalyst from they stripping zone and introducing it into a regeneration zone below a dense phase catalyst level therein, burning deposits from the catalyst with an oxygen-containing gas in the regeneration zone, removing catalyst from gases leaving the, upper part of the regeneration zone prior to depressuring said gases, withdrawing catalyst from the regeneration zone to a conditioning zone, contacting catalyst with hot hydrogen for at least about 5 seconds in the conditioning zone for displacing oxygen, water and sulfur dioxide from the regenerated catalyst, and introducing gases from the upper part of the conditioning zone directly to the upper part of the reaction zone above the dense phase catalyst level so that both the conditioned catalyst introduced at the lower part of the reaction zone and gases introduced therewith will be substantially free from oxygen, Water and sulfur dioxide.

2. The method of claim 1 which, includes the step of cooling the gas from the upper part of the stripping zone before it is introduced above the top of the dense phase in the reaction zone.

3. The method or" claim 1 which includes the step of introducing a cooling fluid into the reaction zone immediately above the dense phase level therein.

4. Apparatus for effecting fluid hydroforming which apparatus comprises a tall insulated reactor designed to withstand high pressure and having a height about 5 to 15 times its diameter, a product outlet at the upper part of the reactor, a distributing grid at the base of said reactor, a charging stock inlet above the distributor grid and about one-half to two reactor diameters above the base the lower part ofthe accumulator vessel to a low point in theregenerator, an inletflline for introducing vair at the base of the regenerator, catalyst separators at the top of ,thcregcnerator and lines for withdrawing catalystfree the gas fromr-the topvof said separators, a catalyst conditioning vessel 50f smaller diameter than the reactor, a standpipe foriintroducing catalyst from a low point in the ,regenerator (spaced from the low point of catalyst introduction.theretolto said conditioning vessel, heating means, comprising atleast one heater for heating recycled hydrogen, a conduit for introducing at least a partof said heated recycled hydrogen from said heating means to thebase of said conditioning vessel, a conduit from said heater for introducingv at least a part of said heated recycledlhydrogen at the base of the reactor, a discharge opening .in said conditioning vessel for introducing conditioned catalysttherefrom above the charging stock inlet-but in' the lowerpart of the reactor, said last named opening .being spaced from said well to prevent catalyst shortscircuiting,,and a connection for introducinga gas atthe bottom of said accumulator vessel.

5." The apparatus of claim 4 which includes a .cooler for cooling gases introduced from the top of the accumulator-vesselto' the upper part of the reactor.

6; The apparatus of claim 4 wherein the heating means includes a first'hydrogen heater for heating hydrogen to abont'700" F., a second hydrogen heater for heating hydrogen to at least about 1200 F., and connections for introducing hydrogenfrom both heaters to said conditioning vessel. v

I 7. Apparatus for effecting fluid hydroforming which apparatus comprises a tall insulated reactor designedto withstand high pressure and having a height about to 15 times its diameter, a product-outletat the upperpart of the reactor, :a distributing grid at the base of said reactor acharging stock'inlet abovethe distributor grid and about one-half to two reactor diameters above the base of the reactor, a catalyst withdrawal Well opening above the distributor grid but below the charging stock inlet, an accumulator vessel mounted at a high level'with respect to said reactor, actransfer line leading from saidwell to said accumulator vessel, connections for introduc ing a carrier gas into said transfer line, a conduit leading from the topof the accumulator vessel to the upper part of the reactor, a regenerator, a standpipe leading from the lower part of the accumulator vessel to'la" low point 1 c in the regenerator, an inlet line for introducing air at the,

base of the regenerator, catalyst separators at the top of the .regenera-tor and lines for withdrawing catalyst-free flue gas from the top of said separators, a catalyst conditioning vessel of smaller diameter than thereactor, a

standpipe, for introducing catalyst from a low point in l the regenerator (spaced-from thelow point of catalyst introduction thereto) -to said conditioning vessel,:heating means comprising at least one heater for heatingrecycled hydrogen, a conduit for introducing. atleast "a part of said heated recycled hydrogen from "said heating means to the basegof said conditioning ve se ajCOHdHit fr m" said heater'for introducing at least a part of said heated recycled hydrogen at the base of thetreacto'r, a discharge openingiin said conditioning vessel for introducing conditioned catalyst therefrom 'above'the' charging stock'inlet but in the lower part of the reactor, said last named open} ing being spacdfromsaid well to'prevent catalyst short circuiting,.and a conduit for conveying gases from the upper part ofthe conditioning vessel directly to the upper part ofthe reactor.

References Cited in the filewof this patent UNITED STATES'PATENTS- V 2,366,372 Voorhees l Jan. 2, 1945- '2,409,35 3 ,-Giuliani;etal. Oct. 15, 1946 j I 2,409,690 i Nicholson 'et a1. Oct. 22, 1946 r 2,414,002 Thomas et -al." l. -'Jan. 7, 1947 2,425,807 Jahnig I 'Al1g. 19,1947 2,447,116 j Collins Aug. 17, 1948 2,471,064 T, Hall et al. "May 24, 1949; ,7 2,472,844 7 'Munday et a1. June 14, 1949. 2,477,740 Grote Aug. 2 19495 2,497,940 Hemminger Feb 21', 11950" 

1. THE METHOD OF EFFECTING FLUID HYDROFORMING WHICH COMPRISES SUPERHEATING A HYDROGEN GAS STREAM TO A TEMPERATURE OF ABOUT 1200 TO 1300* F. AND INTRODUCING THE SUPERHEATED STREAM AT THE BASE OF A REACTION ZONE HAVING A HEIGHT ABOUT 5 TO 15 TIMES ITS DIAMETER, DISTRIBUTING THE SUPERHEATED HYDROGEN ACROSS THE BASE OF SAID ZONE INTO A UNITARY FLUIDIZED CATALYST BED WHICH EXTENDS TO THE UPPER PART OF THE REACTION ZONE, INTRODUCING SUPERHEATED CHARGING STOCK VAPORS CONTAINING A SMALL AMOUNT OF SULFUR DIRECTLY INTO SAID BED AT A LEVEL SPACED FROM THE HYDROGEN INLET BY ABOUT ONE-HALF TO TWO REACTOR DIAMETERS, INTRODUCING CONDITIONED CATALYST AT THE LOWER PART OF THE CATALYST BED, EMPLOYING AN UPWARD GAS VELOCITY IN THE REACTION ZONE TO MAINTAIN THE CATALYST IN DENSE PHASE FLUIDIZED CONDITION AND TO GIVE A BED DEPTH FOR OBTAINING EFFECTIVE HYDROFORMING OF THE CHARGING STOCK AT A TEMPERATURE IN THE RANGE OF ABOUT 850 TO 1000* F, UNDER A PRESSURE OF ABOUT 100 TO 500 P. S. I. G., WITHDRAWING CATALYST FROM THE DENSE PHASE AT A LEVEL BELOW THE CHARGE INLET AND FROM A POINT SPACED FROM THE CATALYST INLET, CONVEYING THE WITHDRAWN CATALYST TO A STRIPPING ZONE AND CONTACTING IT THEREIN WITH A STRIPPING GAS, INTRODUCING GAS FROM THE UPPER PART OF THE STRIPPING ZONE TO THE UPPER PART OF THE REACTION ZONE ABOVE THE DENSE PHASE LEVEL THEREIN, WITHDRWAING CATALYST FROM THE STRIPPING ZONE AND INTRODUCING IT INTO A REGENERATION ZONE BELOW A DENSE PHASE CATALYST LEVEL THEREIN, BURNING DEPOSITS FROM THE CATALYST WITH AN OXYGEN-CONTAINING GAS IN THE REGENERATION ZONE, REMOVING CATALYST FROM GASES LEAVING THE UPPER PART OF THE REGENERATION ZONE PRIOR TO DEPRESSURING SAID GASES, WITHDRAWING CATALYST FROM TE REGENERATION ZONE TO A CONDITIONING ZONE, CONTACTING CATALYST WITH HOT HYDROGEN FOR AT LEAST ABOUT 5 SECONDS IN THE CONDITIONING ZONE FOR DISPLACING OXYGEN, WATER AND SULFUR DIOXIDE FROM THE REGENERATED CATALYST, AND INTRODUCING GASES FROM THE UPPER PART OF THE CONDITIONING ZONE DIRECTLY TO THE UPPER PART OF THE REACTION ZONE ABOVE THE DENSE PHASE CATALYST LEVEL SO THAT BOTH THE CONDITIONED CATALYST INTRODUCED AT THE LOWER PART OF THE REACTION ZONE AND GASES INTRODUCED THEREWITH WILL BE SUBSTANTIALLY FREE FROM OXYGEN, WATER AND SULFUR DIOXIDE. 